1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and, more particularly, to an LCD device and its fabrication method capable of obtaining a wide viewing angle and enhancing an aperture ratio.
2. Discussion of the Related Art
The LCD device, which has been well-known as a high picture quality and low power flat panel display device, includes a thin film transistor (TFT) array substrate and a color filter substrate attached with a uniform interval, in which a liquid crystal layer is formed. Further, the TFT array substrate includes pixels arranged in a matrix form, each unit pixel including a TFT, a pixel electrode and a capacitor. The color filter substrate includes a common electrode formed on the entire surface of the color filter substrate, RGB color filters and a black matrix. The common electrode and the pixel electrode serve to apply electric field to the liquid crystal layer.
An alignment film is formed on facing surfaces of the TFT array substrate and the color filter substrate, and rubbing is performed to arrange the liquid crystal layer in a certain direction. When the electric field is applied between the pixel electrode and the common electrode, liquid crystals rotate due to dielectric anisotropy to transmit or block light according to each unit pixel, thereby displaying a character or an image.
However, the above-described LCD device is a twisted nematic (TN) mode LCD device, a viewing angle of which is narrow. Such a disadvantage results from refractive anisotropy of liquid crystal molecules. That is, with the TN mode, light transmittance is symmetrically distributed with respect to a horizontal viewing angle but is asymmetrically distributed with respect to a vertical viewing angle, thereby causing a range of image inversion and thus narrowing the viewing angle.
In order to solve the problem of viewing angle, there have been proposed a film compensation mode LCD device for compensating the viewing angle with a compensation film, a multi-domain mode LCD device for dividing a pixel into several domains and compensating the viewing angle by making a direction of each main viewing angle of each domain different, an in-plane electric field mode LCD device for forming in-plane electric field by positioning two electrodes on the same substrate, an OCB (Optically Compensated Birefringence mode LCD) device, a vertical alignment (VA) mode LCD device, and the like.
For example, the vertical alignment (VA) mode LCD device utilizes liquid crystals with a negative type dielectric anisotropy and a vertical alignment film. When a voltage is not applied, liquid crystal molecules are arranged such that the longer axis of each molecule is vertical to the planar surface of the alignment film and a polarization plate attached on a substrate is disposed such that a polarization axis is perpendicular to the longer axis of each molecule to display a normally black mode. In contrast, when a voltage is applied, due to characteristics of the negative type liquid crystal molecules being slantedly aligned with respect to electric field, the liquid crystal molecules having their longer axes in a perpendicular direction to the planar surface of the alignment film are moved toward the planar surface of the alignment film to allow light to be transmitted. In the VA mode LCD device, a structure such as a side-electrode or rib, or an electric field distortion slit is formed on a substrate to distort the electric field generated at the liquid crystal layer to position a director of liquid crystal molecules in a desired direction. For example, there is PVA (Pattern Vertical Alignment) or an MVA (Multi-domain Vertical Alignment).
FIGS. 1 and 2 are cross-sectional views showing the unit pixel of a related art VA mode LCD device with a viewing angle improved by the multi-domain. FIG. 1 shows the LCD device utilizing only electric field distortion slits as an electric field distorting unit and FIG. 2 shows the LCD device utilizing a rib.
As shown in FIGS. 1 and 2, a VA mode LCD device 10 includes first and second substrate 1 and 2, and a liquid crystal layer 7 formed therebetween. Though not shown, a plurality of gate lines and data lines are arranged horizontally and vertically to define pixel regions on the first substrate 1, and a TFT is formed at the crossing of the gate line and the data line. A pixel electrode 3 electrically connected with the TFT is formed at the pixel region. A common electrode 4 for generating electric field together with the pixel electrode 3 to drive liquid crystal molecules 9 is formed on the second substrate 2. Though not shown, a black matrix for blocking light leaked from the gate/data lines and TFT and a color filter for implementing color are also formed on the second substrate 2. Electric field distortion slits 6a and 6b for generating distortion of electric field are formed at the pixel electrode 3 and the common electrode 4, respectively. The electric field distortion slits 6a and 6b distort the electric field to divide a domain into several regions to create a multi-domain. In this related art, a rib 8 is formed on the second substrate 2.
In the LCD device 10, when a voltage above a threshold value is applied to the pixel electrode 3 and the common electrode 4, the liquid crystal molecules, which have been arranged such that their longer axes are perpendicular to the planar surface of the substrate, are slanted in a horizontal direction, and therefore, the electric field is distorted by the electric field distortion slit 6b or the rib 8 to make the liquid crystal molecules arranged in a different direction centering around the electric field distortion slit 6b or the rib 8. Accordingly, the liquid crystal directors face each other to compensate the viewing angle, thereby obtaining a wide viewing angle.
However, the related art LCD device has the following problems. If the first and second substrates 1 and 2 are not precisely attached, the position of the electric field distortion slits 6a formed on the pixel electrode and the position of the electric field distortion slit 6a or the rib 8 formed on the common electrode will not be accurate, thereby changing an area ratio of the domain, and degrading viewing angle characteristics and display quality.